Elliott Management pushed pharmaceutical company McKesson Corp. to boost its offer for drug distributor Celesio by just 2.1%, but still made a 13% return on the deal.

According to Market Securities' Timothee de Mierry, the hedge fund accomplished the feat with a side-deal to sell its convertible bonds to McKesson. Elliott, which owned a nearly 25% stake in Celesio, dropped its opposition to McKesson's deal after the company increased its offer by €0.50 per share—and agreed to buy Elliott's convertible bonds. After faltering earlier this month, the deal was finalized last week.

McKesson did not initially disclose how much it paid for the convertibles, but did so in a regulatory filing later.

"We estimate the see-through price is about €30, so they made €165 million altogether on their convertible holding," de Mierry told Reuters.

Elliott accomplished the feat in spite of the fact that it bought most of its Celesio shares at or above McKesson's original offer price. The hedge fund has agreed not to buy any Celesio or McKesson securities or to oppose their boards for five years, and will not seek to disrupt the merger any further, the McKesson filing said.